Gas exchange and photosynthetic light response curves in nematode-infected tomato plants treated with Thuya occidentalis

Abstract

The use of homeopathic formulations on plants may cause changes in plant metabolism and result in disease control by inducing resistance. This work aimed to study the physiological responses of tomato plants infected with nematode (Meloidogyne incognita) and treated with highly diluted preparations of Thuya occidentalis, a homeopathic remedy. The different treatments included T. occidentalis 6CH, 24CH, and 50CH (Centesimal Hahnemanian), a water control (with nematode and without treatment), and an absolute control (no treatment and no nematode). The assay was conducted in a greenhouse using a randomized block design with four replications. Gas exchange parameters were measured at specific times before and after nematode inoculation. Photosynthetic rate, stomatal conductance, transpiration, leaf internal CO2 concentration, and leaf temperature were measured at various photosynthetic photon flux densities. No significant difference was found in the different gas exchange specific measure parameters between the treatments. Untreated infected plants showed an increase in net photosynthesis and in the carboxylation capacity, as shown by the light response curve. Treatment with T. occidentalis 24CH inhibited the increase in CO2 fixation in tomato plants inoculated with M. incognita, leading to a similar behavior as healthy plants, independently of the photon density.